How Did Flowers Evolve?

By Christine Lehman

Overview

How Did Flowers Evolve?

Flowers are the fragrant part of a plant. Flowers can signify romances, celebrate accomplishments, send condolences, deliver apologies, and freshen homes. The real purpose for flowers, however, is to help in plant reproduction. The petals of every type of flower, regardless of how attractive or unattractive they appear, are used to attract pollinators. From the popular showy roses that are popular around Valentine's day to the small, nearly invisible flowers of the duckweed plant, the evolution of flowers has been driven largely by the need to reproduce.

History

Millions of years ago, plants reproduced by means of spores which would float through the air, fall onto land, and grow into a plant identical to its parent. As time progressed, so did the sophisticated nature of plant reproduction. Male and female plants and plant parts developed, which produced pollen (sperm) and ovules (eggs), respectively. Thus, the need for cross-pollination arose, for without cross-pollination, flowers would pollinate themselves and lower genetic variability.

Benefits

Organisms pollinate or cross-pollinate flowers by coming into contact with the male part of the plant, the stamen. The stamen holds pollen which is brushed off by the pollinator and carried to another plant. When the pollinator arrives at the next plant, pollen from the first flower gets transferred to the stigma, or female part, of that flower.

Evolution

Flowers evolved to serve as attractants to organisms. Flowers offer rewards such as nectar or pollen, which can serve as food sources for animals. Occasionally, flowers have evolved to look like insects, and trick other insects of the same species into trying to mate with it, thereby pollinating it in the process.

Flower colors

The color of a flower's petals is determined in part by its pollinator. Hummingbirds are attracted to red flowers, while birds and bees can see other colors and are attracted to a number of different flower species. Some petals have ultraviolet coloration that can be seen by insects, but is invisible to the human eye.

Hummingbird pollinating a flower

Flower shapes

The shape of the flower is also suited to meet the needs of a pollinator. Flowers that are pollinated by hummingbirds and other birds that drink nectar are tubular in shape and have nectar at the base of the tube. Flowers that are pollinated by bees can be different shapes because the bees simply walk across the surface, sticking their tongues in smaller nectar reservoirs. There are plants that are specifically pollinated by bats, ants, butterflies, and many other types of organisms.

Co-evolution

Some plants have very specific pollinators, and have developed flower parts that are suited for a single species of pollinator. This relationship is called co-evolution, two species evolve together. While this relationship works well, the decline of one species is ultimately tied to the decline of another.